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The higher alcohols 2-phenylethanol, tryptophol, and tyrosol are a group of yeast-derived compounds that have been shown to affect the aroma and flavour of fermented beverages. Five variants of the industrial wine strain AWRI796, previously isolated due to their elevated production of the 'rose-like aroma' compound 2-phenylethanol, were characterised during pilot-scale fermentation of a Chardonnay juice. We show that these variants not only increase the concentration of 2-phenylethanol but also modulate the formation of the higher alcohols tryptophol, tyrosol, and methionol, as well as other volatile sulfur compounds derived from methionine, highlighting the connections between yeast nitrogen and sulfur metabolism during fermentation. We also investigate the development of these compounds during wine storage, focusing on the sulfonation of tryptophol. Finally, the sensory properties of wines produced using these strains were quantified at two time points, unravelling differences produced by biologically modulating higher alcohols and the dynamic changes in wine flavour over aging.

When a wine yeast is inoculated into grape juice the potential variation in juice composition that confronts it is huge. Assessing the performance characteristics of the many commercially available wine yeasts in the many possible grape juice compositions is a daunting task. To this end we have developed a barcoded Saccharomyces cerevisiae wine yeast collection to facilitate the task of performance assessment that will contribute to a broader understanding of genotype-phenotype relations. Barcode sequencing of mixed populations is used to monitor strain abundance in different grape juices and grape juice-like environments. Choice of DNA extraction method is shown to affect strain-specific barcode count in this highly related set of S. cerevisiae strains; however, the analytical approach is shown to be robust toward strain dependent variation in DNA extraction efficiency. Of the 38 unique compositional variables assessed, resistance to copper and SO 2 are found to be dominant discriminatory factors in wine yeast performance. Finally, a comparison of competitive fitness profile with performance in single inoculum fermentations reveal strain dependent correspondence of yeast performance using these two different approaches., (Copyright © 2020 Schmidt et al.)

Hydrogen sulfide (H₂S) is a powerful aroma compound largely produced by yeast during fermentation. Its occurrence in wines and other fermented beverages has been associated with off-odors described as rotten egg and/or sewage. While the formation of hydrogen sulfide (H₂S) during fermentation has been extensively studied, it is the final H₂S content of wine that is actually linked to potential off-odors. Nevertheless, factors determining final H₂S content of wine have received little attention, and it is commonly assumed that high H₂S-forming fermentations will result in high final concentrations of H₂S. However, a clear relationship has never been established. In this report, we investigated the contribution of yeast strain and nitrogen addition to H₂S formation during fermentation and its consequent occurrence the resulting wines. Five commercial Saccharomyces cerevisiae wine yeast strains were used to ferment a Chardonnay juice containing 110 mg/l of YAN (yeast assimilable nitrogen), supplemented with di-ammonium phosphate (DAP) to increase YAN concentration to moderate (260 mg/l) and high (410 mg/l) levels. In contrast to the widely reported decrease in H₂S production in response to DAP addition, a non-linear relationship was found such that moderate DAP supplementation resulted in a remarkable increase in H₂S formation by each of the five wine yeasts. H₂S content of the finished wine was affected by yeast strain, YAN, and fermentation vigor. However, we did not observe a correlation between concentration of H₂S in the finished wines and H₂S produced during fermentation, with low-forming fermentations often having relatively high final H₂S and vice versa. Management of H₂S in wine through nitrogen supplementation requires knowledge of initial YAN and yeast H₂S characteristics.

Background and Aims: The significance of oxygen in winemaking has been well established, but knowledge gaps exist regarding the extent and impact passive oxygenation has on chemical and sensory properties during the initial stages. Methods and Results: Using in‐press oxygen monitors, controlling oxygen exposure during the earliest stages of grape processing was shown to be highly effective. This work demonstrated that pressing management has far more impact on wine composition than handling management; the earliest and highest exposure to oxygen has the most profound impact on the composition of the resulting wine compared to the lower levels of repeated exposure typical of normal handling procedures. Furthermore, control of oxygen exposure during post‐pressing operations offers the possibility of modulating specific classes of compounds, described in sensory analysis as floral and confection. Conclusions: Significant modulation of aromatic, phenolic and protein profiles of wine occurred through controlling oxygen exposure during the earliest stages of grape processing. Significance of the Study: This work shows the possible stylistic potential and limitations of oxygen control, albeit with investment in press technology. The understanding of the relative influence of processing variables assessed in this work can be immediately applied by winemakers. [ABSTRACT FROM AUTHOR]